Lipids: Functions and Characteristics

Study Notes

Lipids are a broad group of compounds that are generally soluble in organic solvents but only sparingly soluble in water.

Lipids perform various functions both within the body and in food, including serving as an energy reserve, regulating hormones, transmitting nerve impulses, cushioning vital organs, and transporting fat-soluble nutrients.
In food, lipids serve as an energy source with high caloric density, add texture and taste, and contribute to satiety.

Lipids can be broadly classified into three main groups: simple lipids, complex (or compound) lipids, and derived lipids.

Yield three or more classes of products when hydrolyzed.
Examples: phospholipids, sphingomyelins, cerebrosides, and gangliosides.
Phospholipids yield alcohols, fatty acids (FAs), and phosphoric acid when hydrolyzed.
Sphingomyelins yield sphingosine, FA, phosphate, and choline when hydrolyzed.
Cerebrosides yield sphingosine, FA, and simple sugar when hydrolyzed.
Gangliosides yield sphingosine, FA, and complex carbohydrate moiety that includes sialic acid when hydrolyzed.

Meet the definition of a lipid but do not fit into either simple or compound lipids.
Are non-hydrolyzable.
Examples: carotenoids, sterols (e.g., cholesterol), and fat-soluble vitamins (e.g., tocopherol and vitamin A).

An important lipid in animal biochemical processes that controls the fluidity of membranes.
The precursor for all steroid hormones.
Has a hydrophobic structure made up of adjacent carbon rings.

A diverse, complex chemical group of lipid-type molecules.
Most are multi-cyclic compounds made via successive polymerization and cyclization reactions derived from the 5-C building block isoprene.
Important to flavor and aroma profiles of seasonings, herbs, and fruits.
Classified based on the number of isoprene units incorporated in the basic molecular skeleton.

Dietary or edible lipids are commonly referred to as oils (liquid at room temperature) and fats (solid or semisolid at room temperature).
Oils and fats are largely composed of mixtures of triglycerides.
Triglycerides, also known as triacylglycerols (TAGs), are derivatives of fatty acids (FAs) or esters of three FAs with glycerol.
TAGs make up about 99% of the lipids of plant and animal origin.
Other components of oils and fats may include free fatty acids (FFAs), monoacylglycerols (MAGs), diacylglycerols (DAGs), phospholipids, carotenoids, sterols, and vitamins (A, D, E, K, etc.).